Battery unit, lithium polymer battery using the same, and method for manufacturing lithium polymer battery

ABSTRACT

A battery unit with improved safety measures, a lithium polymer battery using the battery unit, and a method for manufacturing the lithium polymer battery are provided. The lithium polymer battery has a battery unit and a case accommodating the battery unit, wherein the battery unit includes: a cathode plate having a cathode collector and a cathode active material layer coated on at least one surface of the cathode collector; a cathode lead electrically connected to the cathode collector; an anode plate having an anode collector and an anode active material layer coated on at least one surface of the anode collector; an anode lead electrically connected to the anode collector; a separator interposed between the cathode plate and the anode plate, which insulates the cathode plate and the anode plate from each other; and an insulating member formed on at least one of the cathode lead and the anode lead, which prevents a short circuit between the cathode lead and the anode plate or between the anode lead and the cathode plate. In the battery unit, the cathode plate, the separator, and the anode plate are sequentially and repeatedly stacked upon one another. Therefore, the insulating member incorporated in the lithium polymer battery can enhance the safety of the battery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior application Ser. No.10/347,251, filed on Jan. 21, 2003 now U.S. Pat. No. 7,169,505 issuedJan. 30, 2007, which claims the benefit of Korean Patent ApplicationNo.: 2002-0006737, filed Feb. 6, 2002, which are both herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lithium polymer battery, and moreparticularly, to a battery unit configured to prevent a short circuitdue to contact between the electrode leads and the electrode plates, alithium polymer battery using the battery unit, and a method formanufacturing the lithium polymer battery.

2. Description of the Related Art

Lithium secondary batteries have a high energy density per unit weightand an operating voltage of 3.6V or greater, which is three times higherthan nickel-cadmium (Ni—Cd) batteries, nickel-metal hydride (Ni-MH)batteries, and nickel-hydrogen batteries. For these reasons, their usehas become widespread. Lithium secondary batteries can be classifiedinto lithium-ion batteries that use a liquid organic electrolyte andlithium polymer batteries that use a solid polymeric electrolyte.

Specifically, lithium polymer batteries are rather safe and canaccommodate a variety of shapes, especially, in thin film form to complywith the need for small, lightweight, portable electronic products.These properties could not typically be achieved in lithium-ionbatteries. Due to these advantages, the lithium polymer battery hasrecently attracted attention.

Referring to FIGS. 1A and 1B, a conventional lithium polymer battery 10is shown. The conventional lithium polymer battery 10 includes a batteryunit 11, an electrode lead 12 drawn out from the battery unit 11, anelectrode terminal 13 welded to the plurality of electrode leads 12, anda case 14 for accommodating the battery unit 11.

The battery unit 11 has a structure in which a cathode plate, aninsulating separator, and an anode plate are sequentially and repeatedlystacked upon one another. The electrode lead 12 is drawn out from eachof the cathode and anode plates of the battery unit 11. A plurality ofelectrode leads 12 drawn out from the electrode plates of the batteryunit 11 are electrically connected to electrode terminals 13, wherein aportion of the electrode terminal 13 is exposed to the outside of thecase 14. The case 14, shown in FIG. 1A as a pouch shape provides spacefor accommodating the battery unit 11.

The case 14 has a sealing portion 14a to be coupled to another elementto seal the battery unit 11 placed in the case 14. A sealing tape 15 iswound around a portion of the electrode terminals 13 which contacts thesealing portion 14a. Accordingly, as the sealing portion 14a isthermally fused to seal the case 14, the sealing tape 15 is also fusedand bound to internal layers of the case 14, thereby enhancing thehermetic containment of the battery.

However, the conventional lithium polymer battery 10 has the followingproblems. A group of electrode leads 12 extending from electrode plates,which have the same polarity as the electrode leads 12, is bent in aU-shape and then welded to one electrode terminal 13. When theinsulating separator shrinks due to overheating during the manufacturingprocess or during operation of the lithium polymer battery 10, theelectrode leads 12 may contact the electrode plates of the battery unit11 having the opposite polarity to the electrode leads 12, therebycausing one or more short circuits.

In the case where the battery unit 11 has a stacked structure where thecathode and anode plates are stacked upon one another, sharp burrs mayresult at the edges of the electrode leads 12 in cutting a stack of theelectrode plates to form the battery unit 11. The electrode leads 12with such burrs may penetrate one of the insulating separators anddirectly contact electrode plates having the opposite polarity to theelectrode leads 12, resulting in the occurrence of one or more shortcircuits in the battery.

Heat generated when a short circuit occurs in the battery unit 11 istransferred to a thin polymeric layer coated on the inner surface of thecase 14. Accordingly, the thin polymeric film melts, and the electrodeleads 12 electrically contact metal foil which is included as anintermediate structural layer of the case 14. As a result, the case 14gradually corrodes depending on a difference in ionization with respectto the electrode plates of the battery unit 11.

SUMMARY OF THE INVENTION

Accordingly, the invention provides a battery unit with improved safetymeasures, in which electrical contact between electrode plates andelectrode leads that have opposite polarities with respect to each otheris blocked. The invention also includes a lithium polymer battery withthe battery unit, and a method for manufacturing the lithium polymerbattery.

In one embodiment of the present invention, a battery unit includes acathode plate having a cathode collector and a cathode active materiallayer coated on at least one surface of the cathode collector; a cathodelead electrically connected to the cathode collector; an anode platehaving an anode collector and an anode active material layer coated onat least one surface of the anode collector; an anode lead electricallyconnected to the anode collector; a separator interposed between thecathode plate and the anode plate, which insulates the cathode plate andthe anode plate from each other; and an insulating member formed on atleast one of the cathode lead and the anode lead, which prevents a shortcircuit between the cathode lead and the anode plate or between theanode lead and the cathode plate.

In another embodiment, the present invention provides a lithium polymerbattery comprising a battery unit and a case accommodating the batteryunit, wherein the battery unit includes: a cathode plate having acathode collector and a cathode active material layer coated on at leastone surface of the cathode collector; a cathode lead electricallyconnected to the cathode collector; an anode plate having an anodecollector and an anode active material layer coated on at least onesurface of the anode collector; an anode lead electrically connected tothe anode collector; a separator interposed between the cathode plateand the anode plate, which insulates the cathode plate and the anodeplate from each other; and an insulating member formed on at least oneof the cathode lead and the anode lead, which prevents a short circuitbetween the cathode lead and the anode plate or between the anode leadand the cathode plate, and in the battery unit the cathode plate, theseparator, and the anode plate are sequentially repeatedly stacked uponone another.

In yet another embodiment, the present invention provides a method formanufacturing a lithium polymer battery, the method comprising: mixingsource materials for an electrode active material layer; coating atleast one surface of a collector substrate with the mixture of thesource materials in a pattern corresponding to the electrode activematerial layer; cutting the collector substrate with the pattern of theelectrode active material layer into individual collectors;pre-attaching an insulating member to an electrode lead extending fromeach of the collectors; thermally fusing the insulating member to theelectrode lead; and completing formation of an electrode plate includingthe collector which has the electrode active material layer and theelectrode lead which extends from the collector and to which theinsulating member is fused.

In another embodiment, the present invention provides a method formanufacturing a lithium polymer battery, the method comprising: mixingsource materials for an electrode active material layer; coating atleast one surface of a collector substrate with the mixture of thesource materials in a pattern corresponding to the electrode activematerial layer; cutting the collector substrate with the pattern of theelectrode active material layer into individual collectors; dropping acomposition for an insulating member onto an electrode lead extendingfrom each of the collectors; fixing the composition dropped onto theelectrode lead by compression molding to form the insulating member;completing formation of an electrode plate including the collector whichhas the electrode active material layer and the electrode lead whichextends from the collector and on which the insulating member is formedby compression molding.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail exemplary embodiments thereof withreference to the attached drawings.

FIG. 1A is a sectional view of a conventional lithium polymer battery.

FIG. 1B is an enlarged view of portion A of FIG. 1A.

FIG. 2A is an exploded perspective view of a lithium polymer batteryaccording to an embodiment of the present invention.

FIG. 2B is an enlarged view of portion B of FIG. 2A.

FIG. 3 is an exploded perspective view of a battery unit of FIG. 2.

FIG. 4 is a flowchart for illustrating a method for manufacturingelectrode plates for the battery unit of FIG. 2 according to anembodiment of the present invention.

FIG. 5 is a flowchart for illustrating a method for manufacturingelectrode plates for the battery unit of FIG. 2 according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 2A and 2B, a lithium polymer battery 20 according toone embodiment of the present invention is shown. The lithium polymerbattery 20 includes a battery unit 21 and a case 22 for accommodatingthe battery unit 21. The battery unit 21 includes a cathode plate 23, ananode plate 24, and a separator 25 interposed between the cathode plate23 and the anode plate 24 for insulating the cathode plate 23 and theanode plate 24 from each other. In the battery unit 21, the cathodeplate 23, the separator 25, and the anode plate 24 are sequentially andrepeatedly stacked upon one another.

The cathode plate 23 consists of a cathode collector and a cathodeactive material layer coated on at least one surface of the cathodecollector. The anode plate 24 consists of an anode collector and ananode active material layer coated on at least one surface of the anodecollector.

A cathode lead 26 and an anode lead 27 are drawn out from the respectivecathode and anode plates 23 and 24 the ends of the cathode and anodeleads 26 and 27 are welded to respective cathode and anode terminals 28and 29.

The battery unit 21 including the cathode plate 23, the anode plate 24,and the separator 25 is mounted in a space 22a of the case 22. A portionof the cathode and anode terminals 28 and 29 extend out of the case 22.

The case 22 has a sealing portion 22b at which the case 22 containingthe battery unit 21 is sealed. A sealing tape 200 is wound around aportion of the cathode and anode terminals 28 and 29 which contacts thesealing portion 22b. The sealing tape 200 is fused and bound to thesealing portion 22b of the pouch type case 22 during a sealing processby thermal fusion, thereby enhancing the hermitic containment of thebattery. An insulating member 210 is formed around each of the cathodeleads 26 to prevent direct contact with the anode plate 24.

The structure of the secondary battery according to the presentinvention will be described in detail with reference to FIG. 3.

FIG. 3 shows one unit cell of the battery unit 21 of FIG. 2. Referringto FIG. 3, the cathode plate 23 includes a cathode collector 23a formedof expanded metal or punched metal using, for example, aluminum. Frontand rear cathode active material layers 23b and 23c, which include alithium oxide, a binder, a plasticizer, and a conductive material, areformed on both surfaces of the cathode collector 23a.

A cathode lead 26 is drawn out from one corner of the cathode collector23a to a predetermined length. It is preferable that the cathode lead 26be integrally formed with the cathode collector 23a for manufacturingefficiency.

The anode plate 24 is disposed opposite to the cathode plate 23 with theseparator 25 therebetween. The anode plate 24 includes an anodecollector 24a formed of, for example, copper foil. Front and rear anodeactive material layers 24b and 24c, which include a carbonic material, abinder, a plasticizer, and a conductive material, are formed on bothsurfaces of the anode collector 24a.

An anode lead 27 is drawn out to a predetermined length from thediagonally opposite corner of the anode collector 24a with respect tothat corner of the cathode plate 23 from which the anode plate 24extends. It is preferable that the anode lead 27 be integrally formedwith the anode collector 24a.

The insulating member 210 is formed around the cathode lead 26, which isbent in a U-shape to be mounted in the case 22, as shown in FIG. 2. Whenthe cathode lead 26 and the cathode collector 23a are cut together,burrs may result at the edge of the cathode lead 26. It is highly likelythat the burrs of the cathode lead 26 penetrate the separator 25 andcontact the anode plate 24, thereby causing an electrical short.

To prevent these electrical short circuits, a polymeric insulatingmember 210 is formed around the portion of the cathode lead 26 thatseems to likely contact the anode plate 24 having the opposite polarityto the cathode lead 26.

Heat-resistant insulating tapes formed of, for example, polyethylenes orpolypropylenes, can be used as the insulating member 210. Such aninsulating tape may be thermally fused to that portion of the cathodelead 26.

Alternatively, the insulating member 210 can be formed using a polymericresin composition containing, for example, polyethylenes,polypropylenes, or amorphous polyamides. In this case, a predeterminedamount of the polymeric resin composition is dropped onto the cathodelead 26 and set by compression molding.

The insulating member 210 can be attached to the anode lead 27, insteadof the cathode lead 26, or to both the cathode and anode leads 26 and27.

A method for manufacturing electrode plates for the lithium polymerbattery having the structure as described above will be described.

FIG. 4 is a flowchart for illustrating an embodiment of a method formanufacturing electrode plates for the lithium polymer battery accordingto one embodiment of the present invention. As an example, the formationof cathode plates will be described below with reference to FIG. 4. Asshown in FIG. 3, the cathode plate 23 includes the cathode collector 23aand the front and rear cathode active material layers 23b and 23c.Initially, to form the front and rear cathode active material layers 23band 23c, source materials for the cathode active material layers aremixed together. In particular, a lithium oxide as a cathode activematerial, a conductive material, and a plasticizer are mixed with abinder solution to prepare a slurry (S10).

For efficient large-scale production, a plurality of cathode collectors23a are simultaneously formed using a single, large aluminum foil(hereinafter, referred to as a “cathode collector substrate”). Bothsurfaces of the cathode collector substrate are coated with the slurryfor the cathode active material layers 23b and 23c in a patterncorresponding to the shape of the cathode active material layers 23b and23c (S20). Coating both surfaces of the cathode collector substrate withthe slurry for the front and rear cathode active material layers 23b and23c may be performed by casting.

To improve the adhesion of the active material layers to the cathodecollector substrate, which is preferably made of expanded or punchedaluminum, and to reduce the interfacial resistance therebetween for theextended lifespan and enhanced charging/discharging properties of thebattery, foreign materials on the surfaces of the cathode collectorsubstrate are removed prior to coating the cathode collector substratewith the slurry. After coating the slurry for the front and rear cathodeactive material layers 23b and 23c on both surfaces of the cathodecollector substrate, a calendaring process is performed in order toenhance the adhesion of the front and rear cathode active materiallayers 23b and 23c to the cathode collector substrate and to correctthickness deviations that may be present in the front and rear cathodeactive material layers 23b and 23c. The calendaring process ispreferably performed by passing the cathode collector substrate coatedwith the slurry between heating rollers (S30).

Next, the cathode collector substrate with the pattern of the front andrear cathode active material layers 23b and 23c is cut into individualcathode collectors 23a having a predetermined shape using a mold. Eachof the resulting cathode collectors 23a has a cathode lead 26 extendingfrom one edge of the cathode collector (S40).

Next, the insulating member 210, for example, an insulating tape, ispre-attached to the cathode lead 26 (S50). The insulating tape for theinsulating member 210 can be formed of polypropylenes or polyethyleneshaving a low melting point of about 150° C. or less. The insulating tapeincludes a tape layer having a thickness of about 20-70 μm and anadhesive layer coated on the tape layer and having a thickness of about5-20 μm. The insulating member 210 is pre-attached around a portion ofthe cathode lead 26 and preferably has a width of about 2-4 mm.

After the insulating member 210 is pre-attached to the cathode lead 26,the cathode lead 26 is preferably passed between rollers pre-heated to atemperature of about 140-180° C. so that the insulating member 210 isthermally fused to the cathode lead 26 (S60). At this time, there is aneed to control the thickness of the adhesive layer of the insulatingmember 210 so as to prevent agglomeration of the adhesive composition inthe adhesive layer coated on the tape layer as the tape layer is fusedto the cathode lead 26. The temperature of and the space between therollers needs to be uniformly maintained in order to allow easierthermal fusion of the insulating member 210 and so that no foreignmaterials remain on the surfaces of the rollers after fusing.

In step S60, another consideration is to maintain the surface evennessof an insulating member applying roller (not shown) in order to preventthe melted tape layer of the insulating member 210 from spreading towardthe cathode collector 23a. In addition, the rotating rate of theinsulating member applying roller needs to be substantially the same asthe rate at which the cathode collector 23a is moved on a conveyer belt,and the insulating member applying roller needs to apply the insulatingmember 210 in a tensioned state to the cathode lead 26 in order toprevent sagging of the insulating member 210.

Steps S10 through S60 provide a complete cathode plate 23 including thecathode collector 23a which has the front and rear cathode activematerial layers 23b and 23c and the cathode lead 26 which extends fromone side of the cathode collector 23a and to which the insulating member210 for preventing electrical contact between the cathode lead 26 andthe anode plate 24 is thermally fused (S70).

The above-described method for manufacturing the cathode plates for thesecondary battery according to the present invention can be applied tothe formation of anode plates having the opposite polarity to thecathode plates. In manufacturing anode plates, copper foil is preferablyused as an anode collector substrate. Front and rear anode activematerial layers 24b and 24c are formed on both surfaces of the anodecollector 24a, with the anode lead 27 extending from one edge of theanode collector 24a. The insulating member 210 may also be attached tothe anode lead 27. Alternatively, the insulating member 210 may beattached only to the anode lead 27, not to the cathode lead 26.

FIG. 5 is a flowchart for illustrating another embodiment of a methodfor manufacturing electrode plates for the lithium polymer batteryaccording to the pre invention. As an example, the formation of cathodeplates will be described below with reference to FIG. 5.

Initially, source materials for the front and rear cathode activematerial layers 23b and 23c are mixed together. In particular, a lithiumoxide, a plasticizer, and a conductive material are mixed with a bindersolution to prepare a slurry (S110).

The prepared slurry for the front and rear cathode active materiallayers 23b and 23c is coated on the front and rear surfaces of a cathodecollector substrate from which foreign materials have been removedthrough a pre-treatment (S120). Both surfaces of the cathode collectorsubstrate are coated with the slurry for the front and rear cathodeactive material layers 23b and 23c. This step is preferably performed bycasting.

After coating the slurry for the front and rear cathode active materiallayers 23b and 23c on both surfaces of the cathode collector substrate,a calendaring process is performed in order to enhance the adhesion ofthe front and rear cathode active material layers 23b and 23c to thecathode collector substrate (S130). Next, the cathode collectorsubstrate with the front and rear cathode active material layers 23b and23c is cut into individual cathode collectors 23a having a predeterminedshape using a mold. Each of the resulting cathode collectors 23a has acathode lead 26 extending from its one edge (S140). In other words, thecathode lead 26 is integrally formed with the cathode collector 23a.

Next, a composition for the insulating member 210 is dropped onto atleast a portion of the cathode lead 26. The composition for theinsulating member 210 may be a polymeric emulsion containing, forexample, polypropylenes, polyethyelenes, or amorphous polyamides.

Suitable polypropylenes include stereospecific polymers, such as atacticpolymers, syndiotactic polymers, and isotatic polymers, having a meltingpoint of about 120-160° C. and a melt flow index of about 15 g/10 min.Suitable polyethylenes have a degree of crystallinity of about 20-50%and a melt flow index of 5 g/min or greater. Suitable polyethylenes alsoinclude high density polyethylenes having a melting point of about100-160° C., linear low density polyethylenes having a melting point ofabout 100-140° C., and linear low density polyethylenes having a meltingpoint of about 90-120° C.

Preferably, a composition containing 1-5% acrylic acid by weight and thebalance of a polypropylene or polyethylene matrix polymer is coated onthe cathode lead 26 for adhesion enhancement.

Suitable amorphous polyamides may have a melting point of about120-160.degree. C.

The composition for the insulating member is preferably dropped onto thecathode lead 26 through a single or a plurality of screw extruders andthen a temperature regulator (S150). At this time, it is preferable thata precise pressure gauge be attached to the extruder so as to accuratelycontrol the pressure at which the composition for the insulating memberis dispensed.

After the composition for the insulating member 210 is dropped onto thecathode lead 26, compression molding is performed using a mold in orderto shape an insulating member having a preferable width of about 1.5-4.5mm and a preferable length of 2.0-2.5 mm (S160).

In order to easily release the insulating member while keeping it intactand in the desired shape from the mold and onto the cathode lead 26, itis preferable that a release agent be coated on the inside of the moldfor compression molding.

Steps S110 through S160 provide a complete cathode plate 23 includingthe cathode collector 23a which has the front and rear cathode activematerial layers 23b and 23c and the cathode lead 26 which extends fromone edge of the cathode collector 23a and on which the insulating member210 for preventing electrical contact between the cathode lead 26 andthe anode plate 24 is formed by compression molding (S170).

A battery unit according to the present invention and a lithium polymerbattery using the battery unit according to the present invention, whichis manufactured by the above-described method according to the presentinvention, improves the safety and reliability of the battery. It alsoprevents a voltage drop.

While the present invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the appended claims.

What is claimed is:
 1. A method for manufacturing a lithium polymersecondary battery, comprising steps of: mixing source materials for anelectrode active material layer; coating at least one surface of acollector substrate with the mixture of the source materials in apattern corresponding to the electrode active material layer; cuttingthe collector substrate with the pattern of the electrode activematerial layer into individual collectors; attaching an electrodeterminal to an electrode lead winding a sealing tape on a portion of theelectrode terminal that will be in contact with a sealing portion of abattery case; attaching an electrode terminal to an electrode lead;winding a sealing tape on a portion of the electrode terminal that willbe in contact with a sealing portion of a battery case; pre-attaching aninsulating member to the electrode lead extending from each of thecollectors; thermally fusing the insulating member to the electrodelead; and completing formation of an electrode plate including thecollector which has the electrode active material layer and theelectrode lead which extends from the collector and to which theinsulating member is fused.
 2. The method of claim 1, wherein inpre-attaching the insulating member to the electrode lead, apolypropylene tape, a polyethylene tape, or an amorphous polyamide tapeis attached around a portion of the electrode lead.
 3. The method ofclaim 1, wherein in pre-attaching the insulating member to the electrodelead, a polyethylene tape is attached around a portion of the electrodelead.
 4. The method of claim 1, wherein in pre-attaching the insulatingmember to the electrode lead, an amorphous polyamide tape is attachedaround a portion of the electrode lead.
 5. A method for manufacturing alithium polymer secondary battery, comprising: coating at least onesurface of a collector substrate with an electrode active materiallayer; cutting the coated collector substrate into individualcollectors, each individual collector having an electrode lead extendingfrom the collector; attaching an insulating member to the electrodelead; thermally fusing the insulating member to the electrode lead;attaching an electrode terminal to the electrode lead having thethermally fused insulating member, the electrode lead being arrangedbetween the collector and the electrode terminal and winding a sealingtape on a portion of the electrode terminal that will be in contact witha sealing portion of a battery case attaching an electrode terminal tothe electrode lead having the thermally fused insulating member, theelectrode lead being arranged between the collector and the electrodeterminal; and winding a sealing tape on a portion of the electrodeterminal that will be in contact with a sealing portion of a batterycase.
 6. The method of claim 5, wherein attaching the insulating memberto the electrode lead comprises attaching a polypropylene tape, apolyethylene tape, or an amorphous polyamide tape around a portion ofthe electrode lead.
 7. The method of claim 5, wherein attaching theinsulating member to the electrode lead comprises attaching apolyethylene tape around a portion of the electrode lead.
 8. The methodof claim 5, wherein attaching the insulating member to the electrodelead comprises attaching an amorphous polyamide tape around a portion ofthe electrode lead.
 9. The method of claim 5, further comprising windinga sealing tape around a portion of the electrode terminal.
 10. Themethod of claim 5, wherein coating at least one surface of a collectorsubstrate with an electrode active material layer comprises: mixingsource materials for the electrode active material layer; and coatingthe at least one surface of the collector substrate with the mixture ofthe source materials in a pattern corresponding to the electrode activematerial layer.